Consider the S_N2 Reaction of Butyl Bromide with OH^- Ion $\to$

Consider the S_N2 reaction of butyl bromide with OH^- ion. CH₃CH₂CH₂CH₂Br + OH^- $\to$ CH₃CH₂CH₂CH₂OH + Br^-
Assuming no other changes,what effect on the rate would result from simultaneously doubling the concentrations of both butyl bromide and OH- ion?

A) No effect.
B) It would double the rate.
C) It would triple the rate.
D) It would increase the rate four times.
E) It would increase the rate six times.